First of all, since my title isn't self explanatory, what I am trying to do is take a large number and work with it such that overtime it becomes a small number. For example, I am trying to take a number like 400 and say that it came from the number one. But it came from the number 1 in such a way that every 20 hours, the number 1 duplicated creating two. 20 hours later again those two duplicated creating four, another 20 hours and 4 makes 8. Is there a way to do this easily backwards from 400 and see how long it takes to get to one? Also, to throw in a twist, is there a way to figure out the same thing, but every 24 hours one out of the bunch is lost. Like say a Parents having kids, there are 400 kids today and we want to figure out how long it took to make those 400 kids from two people, including the death along the way? Is this possible using math on paper, or would it require something more?